> > For USB or FireWere disks, APM & spindown_time options are ignored, >> other options are applied, force_spindown_time will be applied too. >> There is bug, https://bugs.launchpad.net/bugs/515023 >> explaining why USB and FireWire drives are ignored, however the >> situation might have improved since then. >> > > I was unaware of this bug and never experienced this issue with external > USB drives. I do remember external USB drives going into standby mode > shortly after backup completion, but this does not occur anymore in debian > buster/testing. The drives in question do not support APM so it makes sense > given that -S36 is no longer applied in this case. >
Correction: The external USB drives that used to go into standby mode were not getting any hdparm settings (not event -S36) as they were not used on battery mode and spindown feature is disabled by default for USB drives in recent hdparm versions. This must have been an internal feature from WD as documented here: https://support-en.wd.com/app/answers/detail/a_id/16047 The fact that automatic spindown does not work anymore for these drives in buster/testing may indicate that there is some form of system noise (but somehow this noise would not be sufficient to wake up the drives after hdparm -y) or that something else is actively disabling automatic spindown.
